1. Filed of Invention
The present invention relates to a power converter, and more particularly, relates to a synchronous rectifier for a resonant switching power converter.
2. Description of Related Art
FIG. 1 shows a schematic circuit of a resonant switching power converter. The resonant switching power converter includes a transformer 10 to provide isolation from a line input voltage VIN to an output voltage VO of the resonant switching power converter for safety. Switches 20 and 30 develop a half bridge circuit to switch a resonant tank and the transformer 10. An inductor 5 and a capacitor 40 form the resonant tank. The inductor 5 can be an inductance device or the leakage inductance of a primary winding NP of the transformer 10. The inductance L of the inductor 5 and the capacitance C of the capacitor 40 determine a resonance frequency f0 of the resonant tank.
                              f          0                =                  1                      2            ⁢            π            ⁢                                          L                ×                C                                                                        (        1        )            
The transformer 10 transfers the energy from the primary winding NP to secondary windings NS1, NS2 of the transformer 10. Rectifiers 61, 62 and a capacitor 65 perform the rectifying and filtering function to the transformer 10 for generating the output voltage VO (DC voltage) at the output of the power converter. The detailed skill of the resonant switching power converter can be found in a text book titled “Resonant Power Converters” by Marian K. Kazimierczuk and Dariusz Czarkowski, 1995 by John Wiley & Sons, Inc.
Although the resonant switching of the power converter can achieve high efficiency and low EMI (electric-magnetic interference) performance, a forward voltage of rectifiers 61 and 62 still causes significant power losses. The present invention is accordingly directed to a synchronous rectifier for a resonant switching power converter to achieve higher efficiency.